The chair of Iran's Ambassador to the International Atomic Energy Agency (IAEA), Ali Asghar Soltanieh remains empty at the start of the IAEA board of governors meeting Tuesday at the International Center in Vienna, Austria. (ASSOCIATED PRESS / Ronald Zak)

JERUSALEM (AP) — Israel is sounding increasingly agitated over what it views as American dithering with economic sanctions too weak to force Iran to end its suspected drive toward nuclear weapons.

In a clear message aimed at the White House, Prime Minister Benjamin Netanyahu on Tuesday criticized what he said was the world’s failure to spell out what would provoke a U.S.-led military strike against Iranian nuclear facilities. The comments came in response to U.S. refusals in recent days to set “red lines” for Tehran.

With his strong words, Netanyahu is taking a bold gamble. He clearly hopes to rattle the U.S. into doing more, for fear that Israel might otherwise soon attack Iran on its own. But he risks antagonizing President Barack Obama during a re-election campaign and straining relations with Israel’s closest and most important ally. Relations between the two leaders have often been tense in the past.

The White House said that Obama and Netanyahu spoke by telephone for an hour Tuesday night and reaffirmed that the countries are united in their determination to prevent Iran from obtaining a nuclear weapon. The two leaders agreed to continue “close consultations going forward” regarding Iran’s nuclear ambitions, the White House said.

The White House also denied published reports that Obama had rejected Netanyahu’s request to meet with Obama in Washington next week. The White House says no such request was made or rejected.

Israeli officials say American politics do not factor into their thinking, but that the sense of urgency is so grave that the world cannot hold its breath until after the November election.

“The world tells Israel, ‘Wait. There’s still time,”’ Netanyahu said Tuesday. “And I say: ‘Wait for what? Wait until when?’ Those in the international community who refuse to put red lines before Iran don’t have a moral right to place a red light before Israel.”

Israel views a nuclear-armed Iran as a mortal threat, citing Iran’s persistent calls for the destruction of the Jewish state, its development of missiles capable of striking Israel, and Iranian support for Arab militant groups.

Tehran insists its nuclear program is for peaceful purposes only.

Although the United States has accused Iran of trying to develop nuclear weapon capability under the cover of a peaceful program, the Obama administration has said it does not believe Iran has decided whether to build an atomic bomb — if it in fact develops the ability to do so.

Israeli officials believe time is running short with Iran moving perilously close to reaching weapons capability. They point to Iranian enrichment of uranium, a key ingredient in building a bomb, the movement of Iranian nuclear research facilities to fortified underground bunkers impervious to attack, and Iran’s refusal to open its facilities to U.N. inspectors.

On Tuesday, diplomats told The Associated Press that the U.N. atomic agency has received new and significant intelligence over the past month that Iran has advanced its work on calculating the destructive power of an atomic warhead through a series of computer models within the past three years.

The diplomats who spoke to the AP said the information came from Israel, the United States and at least two other Western countries They demanded anonymity because they were not authorized to discuss classified information member countries make available to the IAEA.

The information could strengthen concerns that Iran has continued weapons work into the recent past and may be continuing to do so. Because computer modeling work is normally accompanied by physical tests of the components that go into nuclear weapons, it would also buttress fears by the International Atomic Energy Agency that Tehran is advancing its weapons research on multiple fronts.

“The two go hand in hand,” said David Albright, whose Washington-based Institute for Science and International Security is a frequent go-to source on Iran for Congress and other U.S. government branches.

In Tehran, Foreign Ministry spokesman Rahmin Mehmanparast told reporters that Iran will start answering the agency’s “questions and concerns” only when “our rights and security issues” are recognized.

Israel says such evidence is concrete proof that Iran is well on its way to reaching weapons capability, perhaps in the coming months.

Differences with the U.S. over how to deal with Iran have boiled over into palpable tensions in recent weeks.

Earlier this week, U.S. State Department spokeswoman Victoria Nuland said “it is not useful” to be setting deadlines or outlining “red lines.” She also noted that Obama has stated unequivocally that the United States will not allow Iran to obtain a nuclear weapon.

On Tuesday, she said the Iranian situation is a matter of “intense discussion” with Israel. She declined to elaborate, saying she did not want to conduct diplomacy in public.

But privately, U.S. officials have bristled at how Israel has publicly played up the differences and publicly lectured Washington on its responsibilities.

They have also been irked by what they see is Netanyahu’s attempts to exploit the campaign season to push the U.S. into difficult positions. The officials spoke on condition of anonymity because they were discussing a sensitive diplomatic matter.

Though they stopped short of accusing Netanyahu of taking sides in the election, the Israeli prime minister has a longtime relationship with Republican candidate Mitt Romney and with Sheldon Adelson, a casino magnate and top donor to the Republican Party. Romney, who visited Israel in July, has repeatedly criticized Obama’s handling of the nuclear issue.

Obama and Netanyahu have long had a rocky relationship, because of policy differences and a lack of personal chemistry. In one famous incident, a frustrated Obama left a White House meeting with Netanyahu to go eat dinner with his family.

U.S. and Israeli officials confirmed Tuesday that Obama would not meet with Netanyahu when the Israeli leader goes to New York for the U.N. General Assembly later this month. Both sides cited scheduling issues and rejected suggestions that Netanyahu had been snubbed.

In a veiled criticism of Netanyahu, his own defense minister, Ehud Barak said preserving good relations with the U.S. was essential and that all disagreements should be handled quietly.

“These differences should be smoothed over, between us, behind closed doors. We should not forget that the U.S. is the main ally of Israel,” Barak said.

The U.S. has led efforts in the U.N. Security Council to impose several rounds of economic sanctions on Tehran. In July, the European Union banned oil imports from Iran, just after the U.S. enacted tough measures against Iran’s central bank.

While there are signs that the sanctions are harming Iran’s economy, Israeli officials believe it has not altered their pursuit of a nuclear bomb.

Israelis are astounded that Iran continues to be one of the leading oil producers, because exports have continued almost unabated to China, India and other points in Asia. Israel yearns for even tighter oil sanctions and a total boycott of Iran’s central bank, crippling its ability to conduct trade.

The Israeli efforts may be bearing some fruit: Last week several European Union foreign ministers said they would support tougher sanctions on Iran. And Canada on Friday severed diplomatic relations with Iran, accusing the Islamic Republic of being the most significant threat to world peace. An Iranian semi-official news agency says Iran expects more countries to follow Canada’s example and close their embassies in Tehran.

Looming in the background is Israel’s threat to use force against Iran, a risky operation that could set off mayhem across the region. U.S. officials have made clear they oppose a unilateral Israeli attack. The U.S. military chief, Gen. Martin Dempsey, recently said he would “not want to be complicit” in such an assault.

The window for Israeli military action is more limited than for the Americans, who possess more powerful “bunker-busting” bombs.

For that reason, the Israelis believe a clear “red line” set by the U.S. would not only send a powerful message to Iran, it would also reduce the need for military action.

“It could be argued that the Iranian nuclear program has actually accelerated in recent weeks and months. That’s why a very firm posture at this time is utterly critical to make diplomacy work,” said Dore Gold, a former Israeli ambassador to the United Nations.

Gold currently heads the Jerusalem Center for Public Affairs, a private think tank, but often acts as an informal adviser to Netanyahu.

Israel itself has not publicly defined its own red lines. Officials say that by doing so, they would essentially be telling the world when it is going to attack.

But Gold said potential red lines for the Americans would be an Iranian decision to enrich uranium beyond the current level of 20 percent, a clear signal they are on the road to weapons, or the accumulation of specific quantities of lower enriched materials.

Gold played down the differences with the U.S. “Basically we are in full agreement about how this is supposed to turn out. But there is a serious problem with respect to the strategy over how to influence Iran,” he said.